xymol, lexol, detail questions

I'm getting ready to detail my recently acquired black 91 90q.
Exterior:
PO used Xymol. I haven't used Xymol before; I hear that it's a pain in
the butt to use. Any major disadvantages to using a different kind of
wax instead? I've used Meguire's #26 paste on my red VW and have been
happy with the results, but from what I understand Meguire's is a
carnauba wax and Xymol isn't (I may be wrong). Bad to mix?
btw anybody used that clay stuff I see in the Griot's Garage catalog?
Worth it? What the heck is it? This is the first black car I've owned
and I'm very paranoid about swirl marks etc -- car looks pretty good
now (considering the age) and I don't want to screw it up.
Interior:
Lexol: again, I haven't used it, but I hear it's _the_ stuff to use on
leather. I'm OK using it, but re: the dash and door areas-- are these
leather and/or is it OK to use the Lexol cleaner and conditioner on
these areas?
Thanks much for any tips.
--Jonathan